1. Field of the Invention
The present invention relates to an imaging apparatus and more particularly to a technique that protects an image pickup element from being damaged and deteriorated due to a negative voltage at the time when power source is turned off.
2. Description of the Related Art
In conventional imaging apparatuses such as digital cameras, Charge Coupled Device (CCD) is widely used as an Image pickup element. CCD is driven by horizontal and vertical transfer driving signals, i.e. a horizontal transfer clock signal and vertical transfer clock signal, wherein the horizontal and vertical transfer driving signals are supplied to CCD in accordance with a timing signal generated by a timing generator (TG).
The horizontal transfer clock signal is a two-phase driving signal to be applied to CCD from a horizontal driver. The vertical transfer clock signal is a multi-phase driving signal (for example, four-phase driving signal) to be applied to CCD from a vertical driver. The vertical transfer clock signal comprises three clock signals having a positive level, a negative level and an intermediate level, respectively, wherein these levels are +15 V, −7 V and 0 V. In short, while the imaging apparatus is in a recording mode, a high positive voltage and a high negative voltage are applied to CCD.
In the imaging apparatus described above, when the power source is turned off, thereby making a power source circuit cease supplying electric power to CCD, a forward bias is applied to a substrate of CCD, allowing current flow through CCD in a forward direction whereby CCD is damaged or deteriorated. Therefore, when the power source is turned off, it is necessary to rapidly make a negative potential in the power supply circuit go down to the ground level. But this process needs much time.
To solve the above disadvantage, there has been proposed a technique, in which a discharging circuit is separately proved, that connects a power line for applying a negative voltage to CCD to the ground according to need, and the power line is grounded in conjunction with operation for ceasing power supply from the power supply circuit to various parts in the imaging apparatus.
However, in the arrangement where the discharging circuit is proved between the power line for applying a negative voltage to CCD and the ground, it is necessary to secure a space on the substrate for installing parts for constructing the discharging circuit. Therefore, such arrangement involves problems that prevent the imaging apparatus from being made small in size.
The present invention has been made to solve problems involved in conventional apparatuses, and has an object to provide an imaging apparatus which can be made compact in size and protects the image pickup element from damage and deterioration due to a negative power voltage.